3D printed boats

For the past year or so, I’ve been collaborating with my Australian friend, Selwyn Holland, in what we think is a project that represents the future of Open Class development.

That may sound like hyperbole, but we have been able to combine my design work and Selwyn’s engineering to produce 3D-printed boats. I realize that a number of you have printed fittings successfully, and some have experimented with hulls, but Selwyn’s extensive experimentation and testing have made 3D printing a viable alternative to any other construction method…and a better one than most.

Here is a picture of one of our RG65 prototypes on the water:

If that intrigues you, check out his new website here https://3dprintedradioyachts.com/

Still having fun with toy boats…Bill

Hi Bill,
yes I’m intrigued and skeptic at the same time, but always curious !
Most intriguing me are the weight, strength and costs once applied to a larger boat like a class M.
Ageing effects ?
I shall read the content of the link…

Claudio, I understand the skepticism…but this really works.

The largest boat we have on the water is an IOM…but Selwyn will be doing a 10R when time permits. A couple of test hulls were printed. Eventually, I think we will do all of the International classes. This picture is a test Selwyn ran back in October. With what we’ve learned since, I will redesign the deck to improve the quality and Selwyn will be able to print a better finish. The test demonstrated that large hulls are very doable, but it made sense to focus on the smaller classes until we get through our learning curve.

The weight and strength are no problem…comparable to carbon hulls. We waited to go public with this until we (mostly Selwyn) worked out the kinks and until we had boats that proved they could win races. Once the initial investment is made in the technology, printing a hull is dirt cheap. Of course, this is too new to know about the effects of aging.

Since you already have the CAD skills, you just need to find a friend (like I did) who has a good printer. Even working across the globe, Selwyn can ask me for a change, I can do it and send it via email, and he can have it printing the next day. The slowest part of our turnaround time is when he has to send me stuff through snail mail.


Hi Bill,
I went reading the paper and really found very interesting.
Having said that I do still believe that the end quality of the product is very similar to what I have already seen in various shops selling extruded ABS type hull. To get it stronger are also heavy in spite of what expected.
If the Hulls are longer then the permissible height of the printer, my understanding unless wrong, is that it is necessary to produce various parts (sleeves) to be joined later to get the Full Hull.
For this material PLA nothing it is said about the resistance against UV. Probably is ‘mandatory’ to cover it with UV resistance paint to avoid brittleness after few months. ABS is known to be suffering from UV.
Certainly is a very fast and clean method of construction, no sanding although the surface finish may be not the same as a mirror surface with a rugosity of less then 5µm, as Reynolds would suggest !!!.
This material is also shrinking during operations of about 1% and for a class M correspond to 12.9mm in length and equivalent % in width. These variations should be anticipated in the design or not ?
I was expecting to read about bulb construction and obtained weights.
Anyhow the technique is very interesting for our hobby.
I wonder what could be the hull weight of a class M bare hull, examples given in attachments

Claudio, you are drawing me into a comparison of materials…but I think that is missing the point. Carbon is probably a better material than PLA, but by the time you carve and polish a plug, make a mold, layup and trim the hull, you could have produced several iterations of your design on the 3D printer. And I’m guessing that by the time my PLA weakens from age or UV rays, I’ll be ready to print another version anyway.

The great thing about printing hulls is not the material used, it’s the process…the flexibility it gives you to design and produce with very quick turnaround and very low cost. If you build a hull with conventional techniques, then decide to change the rocker a bit, you have to basically start the lengthy process all over…probably taking a month to get a new version of your hull. With 3D printing, you can do that in a matter of hours…not weeks.

3D printing also offers a much lower cost of entry into something like the Marblehead class. Many people can’t afford to buy a commercial M hull, and are afraid that, if they did, it would be obsolete in two years. 3D printing is a way to ensure that an M hull is affordable, and that a new version can be easily afforded when the time comes to change.

Selwyn and I aren’t trying to sell anything, or convert people who are comfortable making plugs and molds and laying up carbon fiber, or put commercial hull suppliers out of business. We are offering an alternative to those methods for those who are uncomfortable with the high effort of other methods and the high cost of commercial hulls.

It is the ability to quickly go from drawing board to prototype testing to finished version at very low cost that is revolutionary…it’s a designers dream come true.

As time goes on, Selwyn’s website will offer more how-to articles and more info about our experiences with the process and with our boats. I also plan to do an article on the design process I use working in FreeShip, as well as provide files that people can use to print my designs if they don’t want to learn to develop their own. This is the start of our exploration into this exciting technology…not the end.


btw…You are asking for comparisons for an M hull, which we haven’t done as yet. You have built Footys, and Selwyn did give some examples of the Footy hull weights that you could use for comparison against what you have built. They certainly compare favorably to Footy hulls I have made…and are significantly lighter than ABS hulls that have been available.

We do brush thinned epoxy on our hulls to make them completely watertight…before you ask, that made my 38g Footy hull/deck go up to 40g.

Selwyn’s hulls have a very nice, tight finish…but if you want a perfect finish, PLA is easily sanded.

I just Googled about UV resistance…turns out PLA is highly resistant to UV radiation.

Hi Bill,
I do agree with almost what you say, true if it is breaking it will be easy to make a new one and buy a new printer if needed !

My Footy Esterel Hull was only 56g and was so sturdy that you could play rugby with !!! see picture. Never raced with, was just a manufacturing trial !

I try to imagine what it is in favor and what it is against when the size will get larger.

I recall in Italy a boat of 1 meter imitating the AC Cup. Was made in ABS as many other of the kind and sufficiently heavy that the deck was very close to water when racing. Tens of pictures demonstrate it, but most were very happy to have an (expensive Kit) boat to sail. For sure the error was made at the begin ignoring the ABS weight.

After your first message and since curious by nature, I told myself to get more info about.

I concluded, probably to early and wrongly, that this is not what I’m searching for.
IMHO the technology offered by a 3D printer shall be offering similar characteristics with advantage you have mentioned: construction speed and fast design changes. No doubt about it.

A class M being a racing model shall be competitive (probably the word ‘racing’ is not appropriated unless all the boats are made in the same way like the monotype Dragon Force RG65.

In principle, for a given size and sail surface as per M Rules, the boat shall be as lighter and sturdy as possible to get a chance to be speedy, better if in the hands of good fingers. Similarly with the 10R .

For the time being I’m ignoring if the 3D Printer can satisfy these criteria and I do encourage You and others to continue searching.
Yet, I do not knows as the Bulb Weight is obtained.

Having said that I will continue ‘my learning’ about 3D printing. Don’t forget that I’m over 80’ and spending 3 months to make a boat is getting more tiring !!!

It would be nice if a could get a piece, against payment of course, of a small produced item with a 3D printer and perform a DPA - Destructive Physical Analysis.
All the Best and Happy Easter


what kindof finishing are you doing to the outside of the hull? sanding primer, paint, ect. to get rid of the ridges from printing?


Selwyn has worked so hard to optimize the thickness. speed, and temperature of printing that the ridges can’t really called ridges any more…it really is surprising compared to other 3D work I’ve seen. I guess I’m bragging for him, but my Footy hulls are about 1/64" thickness, so there really can’t be much in the way of ridges or there would be gaps. In our early attempts we had more ridges, and there were some gaps between them…not anymore. We brush thinned epoxy on the outside to make sure the hull is really watertight. The result is a pretty smooth, but not glassy, finish. If someone wants a flawless finish, a little sanding and a final coat is all that is needed. I’m not a big believer in the need for a flawless hull, so for me, the finish is good enough on the Footys that I’m not bothering to sand. I know Selwyn didn’t sand the finish on the Shrink RG65, and it is performing very well against his club fleet.

If I didn’t have too many other things going, I’d have Selwyn print me a Shrink Swing to build and come down and sail with you guys again…hopefully can do at some future date.

I’ll try to get a close-up pic of a Footy print tomorrow so you can see what I mean.


Marc, If you enlarge it, I think this picture shows the finish pretty well. It’s one I posted on the Footy forum of my new hull that is somewhere between AUS and here…should arrive by end of the week.


good call on coating it with some thinned epoxy.

so start to finish on an RG hull how much time?


Remember, both canoe hull and deck print as an integral shape, and print times and quality vary with different printers. That said, Selwyn just sent me this:

"Just ran the data through the software. And this will be about right in reality.

Based on normal flow rates/speed and fine layering to get the nice smooth finish.
Nozzle of 0.3mm gives 20 hours
Nozzle of 0.5mm gives 15 hours

Mass of both come in at around 85 to 95g raw hull. Nice and smooth, rigid and strong."

Here’s a pic of Shrink being assembled:


15-20 hours… that’s not far off a wooden hull… but its time spent waiting and watching, not working…

nice thing is that changing a design and reprinting is a few keystrokes away

Actually for a prototype is rather interesting to modify the forms and the day after having the New Hull.

For what concern the external finish, I’m not sure that will be the one I would search for. Reynolds will not be happy either !! hehe
Thus sanding and painting are probably necessary.

In terms of weight the Trap 65 hull was not far away from 85-95g and a good glossy finish is always welcome as on the 43" !


Again, I’m not quite sure what point you are making. We all know that a good hull can be made by carving a plug, spending a lot of time sanding and polishing, making a mold, and laying up a hull. It looks like you make very nice ones.

The point of Selwyn’s work is to demonstrate, so that others can also learn, how a competitive hull can be made without all that…using a technology that produces a light, rigid, pretty nice hull that can get from drawing board to water in a week or two at low cost.

Do you have reference data that demonstrates a distinct advantage to a glassy hull surface at model boat speeds? I haven’t seen that…but if glassy is what someone wants to get from the 3D printed surface, no problem…it won’t take anywhere near as much work as it does to make a smooth plug. And you do sand and paint those glass hulls, don’t you?


Hi Bill,
I spent more then 35 years in Space Technology and I’m very enthusiastic about everything is close to New Technology, but at the same time I like to think what is the benefit at the End of the Process.

Reported your phrase “… a competitive Hull…”

What do you means by that ?

1 - in terms of costs
2 - in terms of performances in the water, fluidity, friction, roughness …
3 - in terms of easy implementation of the process
4 - in terms of strength/rigidity/twisting
5 - in terms of weight
6 - in terms of durability
7 - in terms of manufacturing time

About Reynolds Number and Frictional resistance the Web is plenty of information, too long to explain here, but as recalled from Book data about Roughness that induce Frictional resistance :

  • Gelcoat polished…1µm
  • Car Body New…5µm
  • Brush paint…20µm
  • Rusted sheet…250µm
  • Concrete finish…1000µm
  • Dirty Hull…5000µm

To note that 37% of the total Frictional Resistance is produced by the Surface finish

As speed increases less shall be the roughness.

So far, my understanding is that this technology allow a ‘fast construction’ if the process is well understood and controlled


By competitive hull, I mean one that can compete successfully in international competition against other entries. I don’t mean that the boat has to finish in first place, but rather that it will show itself to be deserving of racing in the group, staying with the fleet and handling well.

That is what I meant by competitive, but based on his results racing the GM RG65, I think the hulls that Selwyn is producing will show themselves to be competitive in all 7 of your categories.

You seem to be focusing a great deal on surface, but clearly, winning performance is not all about having a shiny hull. I am well aware that there is evidence indicating that hull surface is important in big boats…what I was asking is if you have seen any research results on the effect of hull surface at the low Reynolds numbers at which our models operate. I have heard, but have no evidence, that the available research does not scale down to model size.


is not forbidden to dream, although I would like very much that this technology will become true.

Most of the naval architecture books have plenty of pages dedicated to Frictional Resistance.
True, my phobia is roughness and the pictures seen until now as well seen on Selwyn paper are justifying my remarks.
The thickness evoked of 0.35/0.45 mm are not the ones seen in the pictures that seems closer to 1mm for a 65cm hull (see attachments).
May be thicker and heavy for longer hull ?

Most of the tests carried out are made with “scale models” in towing tank therefore the scale factor are included.

Click on the web : “Reynolds Number” or “Frictional Resistance” and a lot of data become available.

BTW, by performance I do exclude the modeler “Fingers”.

I do also consider for a modeler that the time spent to build a model is part of the game played with a great pleasure … I do not refuse progress, but still I have some reticence to consider “a competitive Hull” in all terms if made with a the 3D printer.

I hope sincerely that the time will prove it or not that I’m wrong !!
May be with a different material then PLA who knows !

For me the roughness is, in my opinion, the critical point of this type of construction that will require hours for sanding, painting, polishing on a surface that is not very sturdy to support manual pressure as seen in the picture and adds weights. My Hulls are supported by the mold.

My regards to Selwyn that I do not have the pleasure to live closer, I will watch the printer working at my place !!!.


OK Claudio,

I understand that you are skeptical and not excited, you’ve made your opinions clear, and I’m not trying to convert you. The only reason I’m replying to your posts is to try to ensure that other readers are not mislead. You have not seen one of these hulls in person, have not handled one, and have not sailed one, so I think some of your concerns are unfounded.

In my opinion, the technology has come true, as demonstrated by Selwyn’s success…though these are the early stages, and it is likely to improve over the next few years.

But enough opinions. Here are some facts:

The finished hulls are as rigid as those built from other materials I have used such as wood, glass, and kevlar.

The PLA material is easy to sand and paint if a glassy surface is desired.

The thickness naturally varies with the size of the model, just as it does when laying up glass or carbon. The result is a hull as light as those typical in the class.

Completed boats have been successfully sailed in three classes: Footy, RG65, and IOM.

Enough said.

In an attempt to be factual, I’ve taken a couple of pictures that I hope will show the texture of one of Selwyn’s Footy hulls. This is straight from the printer. The first is an overall shot. Note the bow, where you can see the thin 1/3mm printing (yes 1/3mm.) The second is a closer view.

To alleviate any concerns about being able to sand the PLA, or that the hull might not be rigid enough to hold up to sanding, I took a couple of hours this afternoon to demonstrate. I took the 26g (yes 26g) Footy hull that I had already coated with thinned epoxy. I sanded it with 220 grit, then sprayed it with rattlecan semi-gloss clear. After drying, I again sanded with 220 grit and re-sprayed. The result is in the following picture. The picture disappoints me, because the plastic shows a pattern underneath the clear, even though the hull is now quite smooth. I guess it is reflecting the pattern from the inner side, but I’m not going to paint it an opaque color just to prove a point…I like the orange. I’m not claiming this is a great finish, I got dust and dog hair in the paint. But it should be obvious that I could get it as smooth as I want by spending some more time…maybe even glassy. The hull took the stress of sanding without a problem…nothing broke or cracked, even though it has no internal supports.

As I was taking those pictures of hulls yesterday, and admiring the finish Selwyn has achieved, it occurred to me that he has got it so tight now that we might not need the epoxy coating. So I threw a pound of weight in the hull (it’s a Footy) taped up the ends, and floated it in the laundry tub…oops, I mean the test tank. Left it there for 12 hours. Opened it up this morning and there is not a single drop of water in it…not one drop!

Awesome work, Selwyn.